The Dose makes the Poison

Author: From ‘The Science Behind Our Food”
Original Lessons
http://science.education.nih.gov/supplements/nih2/chemicals/default.htm. (Chemicals, the Environment and You)
Editor: Stephanie Nardei
Modified for PULSE by Patricia A. Wheeler and Marti Lindsey


1 ½  hours (over three days)


10 -15 minutes


3 400 ml Beakers
1 100 ml Beaker
Food Coloring
Various Chemicals
Handout  1
Handout  2
Handout  3
Handout  4

In groups, they will investigate the effect of a chemical (they choose) on the germination of seeds.  They will calculate % chemical concentrations in water, form a hypothesis, and discuss the ethics of using animals in biomedical research

Students will be able to:

  • Define a “toxic substance.”
  • Define the “science of toxicology.”
  • Differentiate between natural and manmade toxic substances.
  • Develop hypotheses to address the dose response principle
  • Explain toxicological principles governing the safety of a substance.
  • Discuss ethics and practicality of using animals in biomedical research.

National Science Education Standard
Content Standard A – Science as Inquiry

  • Identify questions and concepts that guide scientific investigations
  • Formulate and revise scientific explanations and models using logic and evidence
  • Communicate and defend a scientific argument

Content Standard F- Science in Personal and Social Perspectives
Personal and community health

Arizona Science Education Standards:
Concept 1: Observations, Questions, and Hypotheses

  • PO 2. Develop questions from observations that transition into testable hypotheses.
  • PO 3. Formulate a testable hypothesis.

Concept 2: Scientific Testing (Investigating and Modeling)

  • PO 1. Demonstrate safe and ethical procedures (e.g., use and care of technology, materials, organisms) and behavior in all science inquiry.
  • PO 5. Record observations, notes, sketches, questions, and ideas using tools such as journals, charts, graphs, and computers.

Concept 3: Analysis, Conclusions, and Refinements

  • PO 2. Evaluate whether investigational data support or do not support the proposed hypothesis.

Concept 4: Communication

  • PO 2. Produce graphs that communicate data. (See MHS-S2C1-02)
  • PO 3. Communicate results clearly and logically.
  • PO 4. Support conclusions with logical scientific arguments.

Teacher Background
Hardly a week goes by without hearing that a chemical may potentially threaten our health—pesticides in the food we eat, pollutants in the air we breathe, chemicals in the water we drink, toxic dump sites near our homes. Chemicals make up everything around us. Which chemicals are really dangerous? How much does it take to cause harm? What are the effects of a particular chemical? Cancer? Nervous system damage? Birth defects? Finding scientifically sound answers to these very important questions is what toxicologists do, using the most modern molecular, genetic, and analytical techniques available. Toxicology combines the elements of many scientific disciplines to help us understand the harmful effects of chemicals on living organisms. [TAKEN FROM WIKIPEDIA.]

Related and Resource Websites
Questions People Ask About Animals in Research http://www.the-aps.org/pa/animals/index.htm
Environmental Health Resources section on Basic Toxicology of PULSE. http://pulse.pharmacy.arizona.edu/resources/toxicology/teachers.htm
See also the background section for the ‘The Science Behind Our Food” unit http://apps.caes.uga.edu/sbof/main/lessonPlan/IntroToToxicology.pdf
Dose-Response Relationships In Toxicology http://pmep.cce.cornell.edu/profiles/extoxnet/TIB/dose-response.html, an in-depth overview of dose-response
Green Facts Glossary http://www.greenfacts.org/glossary/def/dose-response-relationship-dose-response.htm, an overview of dose-response for certain chemicals and links to other toxicology terms
Health and the Environment: Food, Farming, & Pesticides http://www.nrdc.org/health/pesticides/default.asp
Questions People Ask About Animals in Research http://www.the-aps.org/pa/animals/index.htm
Write a hypothesis http://www.k12science.org/curriculum/dipproj2/en/lesson1.shtml


Day One
This activity engages the students to the concept of dose-response.  They will determine the effects of various chemicals on the germination of seeds.  Radish seeds are recommended, because they can germinate in 1–3 days.  If you use solid chemicals, make a saturated solution in about 50 mL of water.  Distribute the “Toxicology Lab” (Handouts 1 and 2).  Groups of two to four students are recommended.  Allow about 55 minutes for groups to complete Parts 1 and 2. 

Encourage students to bring substances from home they are interested in testing.
Suggested chemicals available to students:

  • Sucralose (Splenda®)
  • Aspartame (Nutrasweet®)
  • Salt
  • Acetone (use nail polish remover)
  • Caffeine
  • Soda
  • Pine-scented cleaner
  • Window cleaner
  • Vinegar

Suggested chemicals you could make available to students:

  • Lead
  • Nicotine
  • Chlorine
  • Adrenaline or Epinephrine
  • “Acid Rain” (pH of 4.2 – 4.4)
  • Round-up®
  • Insect repellent
  • Alcohol

When storing chemicals, always follow safety guidelines.

Day Two
Students will observe the condition of the seeds in each of their bags, recording the number that have germinated and the number that have not in their science notebooks.  Allow 5 – 10 minutes.

Lead the students in developing their own hypotheses. Tell the students at the end of the project, when they have analyzed the data, they will revisit their hypotheses and decide whether or not the information supports or does not support their hypotheses.

  1. Describe the best form of a written hypothesis using the “if … then” format described in Handout 3.
  2. In small groups with a class discussion, rewrite the statements below in the formal hypothesis format.
    • Chocolate may cause pimples.
    • Salt in soil may affect plant growth.
    • Plant growth may be affected by the color of the light.
    • Bacterial growth may be affected by temperature.
  3. Individually or in small groups students write hypothesis about the growth of the seeds using Handout 3.

Day Three
Students will observe the condition of the seeds in each of their bags, recording the number that have germinated and the number that have not in their science notebooks.  Allow 5 – 10 minutes.

  1. Introduce the topic of using animals in biomedical research by placing this statement on the board or overhead and asking for student responses:

“Virtually every
medical achievement
of the last century
has depended directly
or indirectly on
research in animals.” US Public Health Service

  1. Have the students read and respond to the case study about polio at http://www.the-aps.org/pa/animals/index.htm or give them the booklet from the American Physiological Society at http://www.the-aps.org/pa/animals/index.htm. the response can be a class discussion or entries into their lab notebooks.
  2. Class discussion of Using Animals in Biomedical Research Handout 4 – Explain the importance of this discussion before the toxicology experiment with California Blackworms (the apply lesson of this learning cycle).


Homework or classwork: From the website or the booklet have the students answer the following questions.

See above—they can answer the questions for homework if time does not permit for class work.  

Embedded Assessment
Assess students’ ability to form and evaluate a hypothesis, discuss the concepts of dose, the use of animals in biomedical research and their formal conclusions, based on the experiment.





PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: March 7, 2007
  Page Content: Rachel Hughes
Web Master: Travis Biazo